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A321 Two unsuccessful strong crosswind landing attempts. What was actually going on?
As a passenger on A321 I have recently experienced the following:
The plane took off in strong winds (25-30 knots) and then proceeded to the destination, which it reached in 45 minutes. At first attempt the plane touched the ground with its rear landing gear and then it immediately went full throttle and took off again. After making a circle, the situation repeated after which we flew back to the original port.
The pilot said: "I made the decision to go back because the wind is over 100 km/h, which is above this aircraft limits".
100 km/h is over 53 knots which is way above the limitations of A321.
Crosswind - Takeoff 29 kts
Crosswind - Landing 33 kts
Crosswind with Gusts 38 kts
Tailwind - Takeoff and Landing 10kts
My questions are:

Should the pilot have even attempted to land? Wasn't it too risky?
Should he have even taken off knowing about the weather conditions at the destination airport? How is this kind of decision normally made?
Since takeoff limits are lower than landing, was it safe take back off upon unsuccessful landing attempt? In other words if the winds are bad enough for landing do you want to take off rather than force the plane down and see what happens?

IMO if the wind is head wind it should be fine though. Second question condition at destination may change quickly.

The limits posted are for the crosswind component. For example if you're landing on runway 36 and the wind 53 kts. out of 270° then the crosswind component is the full 53 kts. But if the wind is out of 330° the crosswind component is only 26 kts, and if the wind is out of 360° then it is 0 kts.

Specifically, the crosswind component is wind speed * sin(angle between wind and heading). Also, gusts can cause brief, but very significant changes in wind velocity. Additionally, the sustained wind speeds can also change quickly. It's unlikely that the pilot knew there would be 53 knot winds at the destination before he took off. He probably knew there would be high winds, but there could have been significant differences between the forecasts he had and what actually happened.

Note that the values listed in the flight manual are not normally limits, but only maximum values demonstrated demonstrated during certification.

I'm not sure who qualifies as an expert on xwind landings, but based on 30 years of flying with the last 10 on 747s and having had to deal with xwinds on a regular basis, I see nothing wrong with the pilot's decisions, whether to go in the first place or to return. You never know what the actual conditions are until you get there. Also, a go-around is not the same as a takeoff, even if the wheels are on the ground for a bit. My guess would be that when he had the main gear on, his judgement was that he might be unable to maintain directional control once he lost flying speed, so he lifted off.

@Terry thanks. My thinking was that since I was able to see the weather conditions on my smartphone (winds @ 80 kmh with gusts to 100 kmh) so could the pilot before he took off.
Later the airline said that the winds should die down in 4 hours. Thus, the only real info they had was from the pilot who couldn't land. Otherwise why wait since the conditions haven't changed for the worse?

nothing wrong with "taking a peek". we do it for ceilings and viz in Part 91 all the time. You can also do it for winds.

Based on the provide date, I looked up weather history and the METAR (weather report for pilots) was:

CYUL 110700Z 24033G49KT 15SM -SHSN OVC033 M02/M08 A2937 RMK SC8 SLP948

Which translates, in English, to:
CYUL weather report at 11th day of the month, 0700 UTC time: Winds at 240 degrees at 33 knots gusting to 49 knots, visibility 15 statue miles, little snow, overcast clouds at 3300 feet, temperature -2C, dew point -8C, altimeter 29.37 inches of mercury; Remarks: scattered clouds at 800 feet, sea level pressure 948 milibars
49 knots would be equivalent to 90 km/h, but it is possible that the wind report by the ATC tower was higher at the time of landing.
How much crosswind was there?
Assuming the pilots attempt to land at 24L / 24R, there would be little or no crosswind. However the high wind speed + high variation of wind speed would be a problem: the fluctuation is 16 knots. For a small airliner like a A321, 16 knots of airspeed gain / loss is a lot. The pilot did not feel comfortable putting it down, so he chose to divert. The decision was a wise one: he tried enough (2 attempts) and concluded he'd better get back while there is still fuel left.
(Side story: I once heard a GA pilot who go-around 9 times on the same runway because of high wind. On his 10th approach he crashed)
Was it wise to takeoff?
Yes. Scrolling back the clock a few hours to the time when the pilots would prepare their flight, the weather forecast was:

(...) FM110400 24030G40KT P6SM BKN025 OVC050 (...)

Which translates to: from 0400 UTC time onwards, wind would be 240 degrees at 30 knots gusting to 40. Well, not good, but this was 9 knots below the reported gust when they actually arrived. Moreover, an alternate airport which was within reach and with better winds was chosen. This flight was short, and it is not surprising that on such short flights the alternate is return to the departure airport.
Was it wise to abort the landing and apply full power?
Absolutely! Forcing the plane onto the runway is the exact opposite of what a pilot should do. I will tell you, most (I don't have a number, but a fair guess would be >80%) of the landing accidents occur because the pilots failed to recognize that the aircraft was not fully prepared for landing (gusting winds, too high on approach, flaps not configured etc.). If those pilots chose to apply full power, go around and give it another shot, many lives would have been saved. Many people perceive aborting a landing as "dangerous"; in fact, it's the best thing to do in those situations.

Should the pilot have even attempted to land? Wasn't it too risky?

Ultimately this is the decision of the pilot in command. While airlines have operating procedures (and the pilot can be reprimanded for not following them) the pilot can for any number of reasons attempt a landing, we can spend a lot discussing decision making but my guess is that the pilot felt the conditions were safe to make an attempt at a landing. The problem he encountered (most likely) is that high winds are often accompanied by things like turbulence or wind shear which can make landing dangerous in its own right. Upon his attempt to land he encountered this and decided a go-around and then eventual diversion was the safe choice.

Should he have even taken off knowing about the weather conditions at
  the destination airport? How this kind of decision is normally made?

Yes you do know the conditions when you depart however those are the conditions at the time of departure. Weather can change fast (even in 45 minutes). You could have departed with wind well within limitations and had it unexpectedly kick up. The most tragic and common example of this is VFR rated pilots who depart and encounter IMC in route which often unfortunately leads to accidents.

Since takeoff limits are lower than landing, was it safe take back off
  upon unsuccessful landing attempt? In other words if the winds are bad
  enough for landing do you want to take off rather than force the plane
  down and see what happens?

The limits you have listed are direct cross wind limits, in other words the wind is moving across the runway (90 degrees to the direction of the runway). There is generally no published headwind limit for landing (wind blowing down the runway). There is however a practical limit in the sense that if the wind speed is higher than the maximum speed of the aircraft you will not be able to approach the runway (and will move backwards relative to the ground). This is not really an issue for large planes but for something like a Cessna 150 which can only do about 100Kts it would not be an impossible case although I don't advocate for flying if the ground speed of the wind is over 100kts.
He also did not ever really "land" (even though the mains touched down) he executed a "go around". As long as sufficient runway and airspeed exists when the mains touched down, applying full throttle is more than safe.
In aviation you should never really do something so you can "see what happens" you should always strive to know what will happen as a result of your actions.
If you can provide the airport (so we can know the runway directions) and the wind reports for that day we will better be able to explain what happened.

Thank you for your response.
The Airport is YUL
It was on Jan 11th at 0230 that landing was attempted.
Wind at 0200: 53kmh, dir: 250 degr.
Wind at 0300: 38kmh, dir: 250 degr.

@AlexeiFimine, so given that YUL has runway 24L and 24R, the crosswind component was minimal. That makes it reasonable to attempt the approach. By the way, was the wind 53km/h, or 53kts (= 98 km/h, which would match what you said in the question; METARs normally give wind speed in knots).

@JanHudec it's in kmh
In the question I quoted the pilot. What I provided in the comment comes from the Environment Canada historical data. It's in Km/h.

Sounds like the pilot either exaggerated or got confused, then: 53 kph is <29 knots, within the A320's crosswind landing limits even if it was a crosswind rather than a headwind! It's possible it was gusting, however, and the pilot wasn't happy with the situation.

@JonStory With gust, it may be harder to touch down at the desired place, thus leaving not enough runway to stop safely. Anyway, not landing when not sure to make it safely is a wise decision.

That's exactly what I said? The wind stated should have been fine, but it's possible there were gusts not mentioned on the report

Crosswind "limits" are demonstrated only. So not limiting. For example, Airbus max crosswind for landing on a dry runway is 38 kts including gust(320).
It's not a hard limit, perhaps as wind varies and would be impossible to precisely calculate at the time of touchdown.
Does this mean it's a good idea to attempt landing with a crosswind component of 45 or more kts? There are better solutions but it's a judgement call.
Steady state wind vs gust. Many manufacturers have the crosswind limit steady state. Airbus includes gusts.
Yesterday wind was 280/34 gusting 44 so landing on runway 24 had a 30 kt crosswind. Then short final tower reports 290/34 gusting 54. It's now a 37 kt crosswind. If the runway is covered in snow, the limit is 25 kts including gust.
How can a pilot know that short final. Cant get the charts out.
I have a number in my mind that's the max ahead of time. But as the wind direction shifts it becomes difficult.
All that to say, they aren't hard limits. It's fluid and dynamic. Good judgement is always required and a go around is never a bad decision, although the crowd in the back may think it's a failure or indicative of skill.


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How to control yaw in stick aircraft?
How do you control yaw in aircraft with a stick control?
It seems like forward and back are used for pitch, and left/right are for roll, so where is the yaw?

Foot pedals, almost every plane has them. Same way traditional "yoke" controls affect yaw.

In addition to the selected answer, ground turns are done with the same control on most small aircraft and with a separate tiller on large ones.

The only plane I can think of that doesn’t use rudder pedals to control yaw is the Ercoupe. It was designed to be non-spinnalbe as a safety measure and the rudder and ailerons were linked to the control wheel.

There are a few ways that yaw control is achieved.

The easiest and the first to be successfully used would be to have cables from rudder pedals on each side of the rudder to deflect the control surface and control yaw.

Airplane Flying Handbook pg 2-1

The first application to control yaw unsuccessfully was the development of gears and linkages that will control both roll and yaw with the pilot stick.  It was quickly discovered that there are cases where you may need to use the controls separately.
Yaw damper is an electronic device that sense yaw rate and will provide inputs to the rudder to keep the airplane coordinated.

https://www.gulfcoastavionics.com/images/products/3552/detail/detail.jpg

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


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What's inside the packs? (Airbus a320)
I have some questions about ATA 21, how packs works?... I mean, what's inside them?, what are their mechanims? And How the warm air becomes into cold air?. (On a airbus A320)
I'm starting my major at aeronatics and i don't have any idea about ATAs.
I couldn´t find clear information about it on my lenguage, But found this forum and i hope that somebody can help me.
Thanks.

https://en.wikipedia.org/wiki/Air_cycle_machine

Here's an answer for the B737, from own work compiled from several public sources. The A320 and other airliners are very similar.

The air conditioning packs are Air Cycle Machines (ACM) which remove heat from air through a reverse Brayton cycle. Hot compressed air is cooled and then expanded, which drops the outflow temperature to a temperature cold enough to provide cooling in hot environmental conditions.
The ACMs in the Boeing 737 are 3-wheel units consisting of a compressor, two heat exchangers, a turbine and an impeller fan. Bleed air is cooled in the primary heat exchanger, enters the ACM, is compressed further and cooled again in the secondary heat exchanger. The ACM compressor’s further temperature rise allows for more efficient cooling by the heat exchangers.
Cooling air for the heat exchanger is provided by ram air, via inlets underneath the fuselage, in front of the body/wing intersection. Water is extracted from the cool air, and sprayed into the ram air stream for more efficient cooling via the heat exchangers.
The impeller fan creates cooling air flow when airspeed is low. The impeller fan speed can be controlled independently from the ACM turbine/compressor axis, by the Turbofan Control Valve.

Thank you so much.

This type of system is almost universally used on airplanes with the ability to provide decent bleed flow from the engines.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Refuelling an airbus to maximum
The airbus A350 aircraft when being refuelled seems to drop when the wings are filled.How  much is the drop from empty to full.Thankyou

Are you asking how much the wing tips drop, or how much the entire aircraft drops?

That’s going to depend on a lot of things including how well serviced the struts are, what the existing payload on the aircraft is and whether the aircraft is parked on any sort of grade.
I don’t work the A350, but I work other heavy aircraft and I’ve had them “settle” quite a bit when putting on a full fuel load.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Why did the US Airways Flight 1549 passengers stay on the wings?
Couldn't they use the overwing slides as flotation devices and stay on those instead?

Because they were told to evacuate there, if you take a look at the official audio transcript from the accident:

place both arms through the straps and hug it to your chest. flight
  attendants are pointing out there are a total of eight exits on this
  aircraft, two door exits in front of the aircraft, four window exits
  over the wings, and two door exits in the rear of the aircraft. once
  again, two door exits at the front of the aircraft, four window exits
  over the wings, and two door exits in the rear of the aircraft. each
  door is equipped with an evacuation slide if directed to exit... the
  aircraft jump onto the slide and move away from the aircraft.

The rear exits were largely blocked by water making the forward exits the only ones with slides, those slides were utilized as evidenced by photos included in the report:

(source)
With only half of the slides available the wings also had to be used. The wing slides are intended only for ground landings and do not double as rafts, as per the accident report

According to TSO C-69c, Type IV is a combination inflatable exit ramp
  and wing-to-ground slide. The off-wing ramp/slides were intended to be
  used in the event of a ground, not a water, evacuation.

As such the over wing slides could not be used in this case.

I wasn't aware that the overwing slides were not designed for water evacuation. Thanks!

Could you explain why the over-wing slides were not designed to be used as rafts?

@RobinBennett that is a good topic for another question here. The quote is the full citation from the report and does not offer an explanation. TSO C-69c might offer more explanation. Broadly if the FAA does not require something companies may not build in "extra features" as it may cause them to be subject to a more complex certification process.

Per the accident report from the NTSB, only the four exit slides (two at the forward doors and two at the aft doors) could be used as rafts, as the aircraft was configured for extended overwater operations (EOW). Regulations required there to be enough capacity for all passengers if the largest raft was not usable. Each slide/raft was rated for 44 passengers, or an overload of 55 passengers.
During the ditching, the aft part of the cabin rapidly filled with water, preventing the use of the aft two exits and their slides. This meant that the remaining rafts could hold a maximum of 110 people if overloaded out of the 155 people on board the flight. That would leave at least 45 people on the wings.
The report states that about 87 people were rescued outside the two rafts. Many passengers rushed to the overwing exits, creating a backup, and flight attendants had to ask passengers to come forward to the rafts. The overwing exits are not supposed to be used unless other exits aren't available. There are also life lines to help passengers when out on the wings, but these were not used. Since the flight attendants are located on either end of the plane they were too far away to advise the passengers about this.
The report further discusses that even the two usable rafts were not technically required (the flight was not an EOW route), and the remaining passengers would have been in danger of not surviving the cold water if they had not been rescued so quickly.

"The overwing exits are not supposed to be used unless other exits aren't available." Absurd! What kind of bureaucrat writes a rule telling people how to evacuate a plane filling up with water?

@rclocher3 Presumably, the bureaucrat who knows the over-wing exits are smaller and don't have a flight attendant stationed by them to assist with deployment and egress, rendering them more risky?


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Does the wing always have an adverse pressure gradient along the chord?
I know that there is an adverse pressure gradient on the upper surface of the wing, which leads to boundary layer separation.
Is there any condition under which there is no such adverse pressure gradient on the wing?

Adverse pressure gradient exists even without a stall. On an airfoil the airflow slows as it approaches the trailing edge, therefore increasing in pressure as it goes.

At the trailing edge of the upper surface, you will always have a pressure recovery as low pressure from the upper surface converges toward the high pressure from the bottom surface at its trailing edge. This is the adverse pressure gradient since pressure is increasing along the chord length. The gentler the pressure recovery, the less likely is the airfoil to have an adverse boundary layer velocity profile, which is the source of flow separation and stall.
Source: https://www.researchgate.net/figure/Airfoil-Cp-vs-x-c-curve_fig9_306374523

Since most of the lift is through the suction from the upper surface, I don't think you will encounter a practical airfoil without pressure recovery.


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Why would a turboprop rev down just before going full throttle during takeoff?
The only turbprop I've travelled is the ATR 72. I've noticed that the props' rev go down (for like a second, the sound also goes down) just before engaging full throttle in order to takeoff. I've included a video (video is not mine), this thing happens at 1:40. Why the RPM drops for a sec? Or is this just the sound?

Because the pilot is taxiing the airplane with the props in the beta range (turboprops turn into landsharks if you don’t do this and you end up really riding the brakes to keep the speed down), then on takeoff, the propellers move into a maximum power setting, the engine snarls and slows a bit under the increased workload.

I like the colorful language "landsharks", "engine snarls"

Exactly, it's like the light turns green and you lift off the clutch -- that point where you stop slipping the clutch and it fully engages, the engine slows a bit to fully mesh with the road, but that it increases its torque, so you're not making less power but same power at less RPM, hence the growl.

@Sam As a non-pilot who visits this SE from time to time, those were the words which made me understand what was being said =)

It's because he was taxiing in DISC (discing, or flat pitch making the prop like a big disc), which is in the ground beta range, then coming out of it.
Beta range is a mode where propeller blade angle is directly controlled by the power levers, and the propeller RPM is controlled by an Np governor in the fuel controller modifying gas generator (the engine core) speed to maintain rpm on a fixed schedule, depending on where the power levers are.  Beta range is similar to speed governing on a turbine helicopter, where you change pitch with collective and a governor automatically controls the fuel to keep the rotor RPM constant for you.
Beta range starts just ahead of flight idle (there is no marking for this on the power lever quadrant).  The range forward of idle is "flight beta" and aft of flight idle is "ground beta".  On the non-FADEC PW120 series engines there is a cam called the beta cam (obviously) in the power control linkage (on the propeller control unit on the engine) that triggers the transfer of propeller control between the prop governor/prop lever setting and the power lever/fuel controller once the prop has hit its fine pitch limit and propeller governor is no longer governing.
So to be in beta mode the prop has to be "off the governor" (with no torque and the props set to MAX RPM, the prop is trying to go finer and finer to keep the rpm up, then the blades hit the full fine pitch limit, about 24 degrees, and there's nothing more it can do) and the power lever has to be back just forward of flight idle at which point the beta cam takes over to directly regulate blade angle, from +24 degress to -11 degrees blade angle.  So if you are descending with the engines at or near flight idle you are in flight beta mode.
Once in beta mode the beta cam works with a beta metering valve to regulate fine pitch oil pressure to the prop such that when the power lever is moved, the cam movement displaces the metering valve, causing the prop pitch to change until the input is nullified and blade angle is fixed at a new position.  The cam's profile thus gives a specific blade angle for a given power lever position.
Anyway, what's happening there is engine's torque dropping off momentarily as the engine transfers from prop rpm governing in beta (via the fuel controller Np governor controlling torque) to normal flight mode (rpm controlled by the propeller flyweight governor as set by the prop levers, with the power levers now taking over production of torque) as the Power Levers are moved past about one inch forward of Flight Idle.

I fleshed it out a bit, at the risk of making people catatonic... The beta cam is part of the prop control unit on the engine not the power levers.  There are no beta markings on the power lever quadrant.  Coming in and out of flight beta will be transparent to the crew since very little torque is being produced until you are moving into reverse..

Most likely this is happening after the pilot advances the power lever -- but the power lever controls both throttle (fuel flow, in a turbine), and propeller pitch.
The propeller can change pitch pretty quickly, while the turbine takes longer to increase power (increased fuel flow must produce hotter combuster air, which must then spin up both the turbine-compressor section, and the independent shaft power turbine connected to the gear box and propeller).  Usually, the engine's rotating parts will change RPM faster than the ones that spin the (relatively large) propeller, so you may hear the "whine" or "whistle" of the primary shaft spooling up before the propeller noise starts to rise, possibly even while the propeller is still slowing down from the pitch increase.

It is technically correct, but without mentioning the beta range it is misleading. In the normal range propeller pitch is controlled by the governor and that reacts to RPM, so it can't cause a temporary decrease. However the power levers do control pitch in beta and transition from it, which is where this happens.

In the video you can actually notice that as the sound goes down, the propeller becomes "thicker" — the blades are rotating to increase angle of attack.


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Does a Boeing 747-830 exist and if it does, is there any difference to a 747-8 (748)
Two years ago I've uploaded a video of the Lufthansas Boeing 747 "D-ABYA" to Youtube. I am currently receiving some angry comments on that video because the title reads "747-830 with new Lufthansa livery performs low pass at Hanover Airport". Many people are angry with the label "747-830", telling me that no such thing exists and that the featured airplane is a 747-8 or a 748.
Back when making the video, if I recall correctly, I looked up the type on Jetphotos. It reads "Boeing 747-830". The same is true on Flightradar24. airframes.org tells me the type is B748 and the model is 747-830. However, I could not find a reference to "747-830" on boeing.com.
What are the differences between type and model? Is a type 747-8 always a 747-830? Or are there other models with a similar name (747-8xx)? Am I correct in saying that the airplane is a 747-830?

I guess this is the video. Don't worry too much about angry, ignorant people on the internet (and in real live), don't waste your energy correcting them.

@DeltaLima that's the one. Uploaded it a few years ago, but it gained 99.9% of it's views in the last week. Sometimes the YouTube algorithm can be funny.
Well, I was wondering if the title was wrong, hence the post. And I'm afraid if I don't correct them, other people might read those comments and get wrong information :-)

you could consider explaining the 747-8 / -830 detail in the video description. But those that are fast to comment, are probably slow to read! Grüße aus EDDF

Until 2016 Boeing included customer codes into the aircraft model names. Your example 747-830 decodes as follows:

747: This is the general aircraft series.
-8: The 747-8 variant (in this case, a 747-8I, where I is for Intercontinental, the passenger variant).
30: The customer code for Lufthansa or Condor Flugdienst (see e.g. Wikipedia for a list of customer codes).

So this makes it a Boeing 747-8 produced for Lufthansa (Condor does not have one).
The term B748 is the ICAO code for the 747-8.

Additionally 748 is the IATA code code the 747-8 because IATA is always a letter short.

@Martijn I'm not so sure: the Wikipedia table lists 74H and 74N as the IATA codes for the 747-8I and 747-8F respectively. They don't a give a source though...

Yes, a Boeing 747-830 exists.
There are a variety of codes for airplanes, one of the most common being the ICAO code. It lists the latest model of the 747 as B748.
However, Boing uses an additional, airline-specific code. The number 30 is given to Lufthansa and Condor, so the 747-8 in Lufthansa layout is the 747-830.


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What is the risk of a single skydive?
I've seen many articles that compares the risk of skydiving with other sports or activities like cycling or driving. However, they are very ambiguous in terms of how the risk was calculated (number of jumps, number of km driven, etc). Here is an example:

Image taken from here.
So, how much is the risk of a single jump?
How does that compares with a common activity like driving a car?

Welcome to aviation.SE!

@Pondlife Thanks!

I think that those stats are all supposed to be per "instance" — per jump, per flight, per trip, per boxing match, etc. Some of the activities further down in the original image have annotations like "per mile" or "per flight hour", but none of the sporting ones do.

Doing it one time is kind of like bungee-jumping. If everything works the way it's supposed to, there's little actual risk. On the other hand, if something goes wrong or someone made a mistake somewhere... the result of that risk is death.

Right now your answer appears to be to a question about an average per-jump risk across the entire skydiving population.  Are you interested in that, or in the risk of a first jump, which I believe would be different?  (The question seems ambiguous to me, though obviously the answer isn't).

Presumable you mean the risk of death? Risk is relatively meaningless unless you do it frequently.

I think this is a risk that you cannot assess that way. Statistically, it may be 1:100,000 for a large (infinite) number of samples. However, for a bloody beginner with zero experience, the risk on the first jump likely is more like 1:100 or worse. Risk -- for everything -- goes down drastically after the first few attempts due to having better experience and being less nervous. And then, ironically, after some years, and despite experience it drastically goes up again due to becoming careless (because hey, I know what I'm doing!).

As an ex hang glider pilot, I have to dispute that image anyway. It probably was true for hang gliding back in the 70s, but not any time recently.

The image states something about likelihood, likelihood of what? Accident? Major accident? Fatal accident?

@Mast I put only a small section of the figure, if you follow the link you will see the whole figure and its header "Your chances of dying".

Puzzled by this question I did my own research and found numbers that allows to get a good comparison for year 2016:
According to the United States Parachute Association (USPA), there were 3.2 million jumps in 2016 and 21 fatalities. Therefore, the chances of dying in a single jump were 1 in 152,381.
For a comparison with driving, we can use data from the Insurance Institute for Highway Safety. According to which, in the United States there were on average 1.16 deaths per 100 million vehicle miles traveled.
Crunching those numbers, the chances of dying by driving one km are 1 in 138,103,448. Therefore, to equal those chances to one skydive you have to drive 906 km.
Summarising
In 2016, a single skydiving jump in the US represented the same risk of death as driving 906 km (566 miles).
[UPDATE] Demographics
Many have pointed in that there might be an important component of the risk related with age, experience and how careful a skydiver is.
To approach to an understanding in that regard I've compiled the 147 fatal accidents in the USPA database that happened from 2008 as a result of solo jumps (i.e. not-tandem).
This data do not allow to infer real demographics trends, because I don't know how many total jumps were in each demographic group (I only know how many lead to a fatal accident). However, the visualization of some aspects of the data can be informative.
In the following figure each dot is a fatal accident, and it is plotted based in the numbers of jumps the person involved have performed before the accident (vertical axis) and the age of the person (horizontal axis).
It is clear that the bulk of casualties happen to fairly experienced skydivers (100+ jumps). So, as expected, the more you jump the more chances of dying you have. Note that the vertical axis is logarithmic (so to distinguish between people with relatively small jump counts).

This may lead to think that the first 100 jumps are quite safe, but we can not jump to that conclusion: If you check how many death are there for different jump numbers, you have the following picture

In this plot, the first bar counts deaths during jumps 1 to 50, the second bar for jumps 51 to 100 and so on.
So now it seems that most deaths are in the first 50 jumps. However, that  does not mean that the first 50 jumps are more dangerous, because there were many more jumps corresponding to jump number 1 to 50 than jumps number 900 to 950. So, however informative, this have no real statistical value. And the trend suggesting that jumps become less dangerous as you gain experience might be just an artifact due to the fact that there are more beginner skydivers than experienced ones.

@ Camilo Rada that's brilliant.  As an ex skydiver, it fits, in my opinion.  Now I've always said jumping is probably about as dangerous as motorcycles or maybe less so.  Thing is when you jump, most of the risk of death is from a failure to perform when required, like after a malfunction (the probability of a double malfunction is pretty microscopic) whereas on a motorcycle, the risks are all around you and many are out of your control.

@JohnK Indeed. I just finished an skydiving course, and that's why I found myself seeking for this stats in an attempt to silence with facts all those who tell me that I'm crazy and that skydiving is like wishing to die.

That's actually a decent way to put a number on it. There's always the apples to oranges problem between driving and aviation. One measures stats in miles, the other in hours. So figuring that I drive around 1200 miles a week, that's equivalent to about 2 jumps/week in risk. I just might take up skydiving now!

@JohnK So what you're saying is, you should skydive to work instead of riding a motorcycle... ;-)

@ Micheal I was jumping in my 20s and am now in my 60s and I don't think I'd have the balls to do it today although I'm still flying airplanes and gliders.  But really, if one of my sons announced he was jumping or getting a street bike, I'd be less concerned if he was jumping.

Interesting take but selection bias is strong in this answer. Teenagers have three times the driving fatality rate of those 20 and older; few teens skydive. Drivers come from every walk of life; the top ten demos (70%) for skydivers are military, self-employed, engineers, skydiving professionals, health professionals, computer engineers, management, business/finance, sales/marketing, and aviation. Not surprising since the sport is fairly expensive and completely discretionary. Correcting for demographics would give a completely different answer.

@JohnK Equipment failure causes 50% of skydiving fatalities, so the probability of a double malfunction can't be that microscopic.

Would be interesting to know if the chances of dying are the same in the 1st and 1000th jump. But then, n = 21 isn't enough for that.

@Pilothead If there's a 1:552 chance of equipment failure independently, there's a 1:304704 chance of a double equipment failure. Half that gives you 1:152352, close enough to the actual stat.

@Pilothead Double likelihood malfunction is indeed microscopic. Malfunctions are the cause of so many death due to people failing to properly handle the malfunction of the main chute. Or pulling too low, so they don't give themselves time to handle the malfunction or cutaway and pull the reserve.

@DonQuiKong I didn't answer your doubt but added something about it

Good point... dealing with an emergency with a parachute is a bit more complex than dealing with an emergency with a car. The inexperienced may well freeze up in terror, or may not even recognize that a problem needs immediate attention.

Here is another way to understand risk perception in skydiving vs driving.
In skydiving, equipment malfunction is the cause of 50% of deaths. The highly regulated automobile industry would never stand for this. It would be deemed unnecessary and engineered out of the products. Collisions, landing problems, and other account for the other 50%.
In driving, almost none of the fatalities are equipment related as it doesn't even rate a one percent causality. Drunk driving, speeding, distractions and weather cause nearly all traffic fatalities.
In other words, if you are a careful driver you can eliminate virtually all risk of death from your own driving. If you are a careful skydiver, at best you can only eliminate half the risk.
My guess is that few skydivers jump drunk, or exhausted and just trying to get home, or in a downpour. The 900km risk comparison might be fifty times too generous when applied to conscientious people, which I would assume skydivers already are. 45,000km might be more reasonable given the <1% vs 50% equipment failure ratio, and this is more than two years of driving for the average person. This is also more in line with general perception of risk.

I agree with the general sentiment, but I’m wondering: How many of the skydiving equipment failures could be avoided by careful inspection? How many occur because the equipment is operated wrongly or used in the wrong circumstances?

@Michael I think this is the point. Cars don't have to be inspected every time you use them; they are pretty much idiot proof. Safety equipment costs about $2k per car, and that doesn't count all the engineering to make cars durable and reliable. Automatic chute deployment is one step skydiving is taking in this direction.

"In other words, if you are a careful driver you can eliminate virtually all risk of death from driving." Sorry, this is just not true. No amount of care will eliminate much of the risk to you from other people who are drunk, speeding, or distracted.

@DavidSchwartz You are correct. I should have said "risk of death from your own driving". Fixed.

I think you are stretching the numbers a lot for the sake of the argument. From one side, as you already acknowledge, there is a lot of risk in driving that you cannot avoid by being careful. The the 50% stat is based on one year only (n=24), the same article say 11 to 50%. And lastly and more important those are MAIN parachute malfunctions. Arguably, a careful skydiver should be able to deploy the reserve and land safely if the main parachute malfunctions.

@Pilothead Look at the demographics update I did in my answer

You jump with a main chute and a reserve chute.  The odds for either one of these failing are roughly 1 in 1000.  This give approx a 1:1,000,000 chance both fail and you fall to your death.
That’s the risk of a parachute failure.  It does not account for risks associated with jump plane crashes, mid air collisions during the ride up, free fall or canopy deployment, improper landing, etc

Or a car accident on the way to or from the airfield. As per above answer, if you drive 10 KM to the airfield and another 10 KM back, then 50 such trips equal the risk of a single skydive.

@Carlo Felicione the failure probability of a professionally inspected, packed and rarely used reserve is a fraction of the rate for a repetitively user packed main where most malfunctions are due to packing errors and canopy wear and tear.   I'd say the probability of a random double mal is quite a bit better than 1 in 1 mil.

This reminds of Ed Link that wanted to save Air Force pilots lives so he invented the Link Trainer (1929). Later he learned more pilots died driving to and from the airport and became a major force in car seat belt reform.

Reference for 1 in 1000 odds for both main and reserve parachute malfunction please. One in 150k jumps results in death, and equipment malfunction causes half of those. One in a million is more than three times too rare.

Like most aviation related risks, most people want to know the risk of random failures beyond the person's control, which filters out many performance related failure modes.  When I was jumping in the late 70s it was expected you'd have a mal by 5-700 jumps and the average experienced jumper with a couple thousand had had 2 or 3.  The fatalities generally follow screw ups in handling the malfunction.  Try to find a case of a reserve, PROPERLY DEPLOYED, failing and it's vanishingly rare.   Unlike bikes where you can be taken out by other drivers at any time, in jumping it's almost all on you.

I don't think the math is as simple as this.  Aren't there some main chute malfunctions that prevent a clean cutaway, and therefore cause risk of the backup chute failing to deploy properly even if it was otherwise fine?


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How can you relate structural forces to load factors and inertia force
Our professor in aircraft structures asked us to research how can you relate structural forces to load factors and inertia forces and i dont have a clue. Help

Start with $F=ma$ and then come back when you get stuck.

F=ma is a great place to start!  The other one is torque = force x lever arm length.
One might start by considering what needs to be built, a jet fighter or a recreational biplane.
Limiting factors eventually are pilot comfort, speed, and manuverability.  You build a flight envelope profile:  how fast, how slow, how high, (we all get) how low.
From these parameters (and with the help of more mathmaticly oriented colleagues found here) we now set maximum loads on the aircraft, usually at maximum speed and mauverability.
Notice that inertia is a function of mass.  F=ma. a=F/m.  If it is heavier the acceleration
is less.  This would work into roll rates with heavier wing tips.
Torque would work into control surface area and distance from CG, as well as weight distribution.
Structural forces must be sufficient (safety margins are suggested) to meet all load forces.
Before wading into the Math, I would present the design application and determine reasonable limits and safety margins.
In the real world there is nothing wrong with forming a team to solve these issues.


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What's a typical first lesson of glider flying like?
What is a typical first lesson for glider flying like? Does it usually include a pre-flight mini lecture on basic theories at all, or if not pre-flight, do instructors usually spend some time on the ground teaching related theories at some point of the lessons?

I understand it may appear as primarily opinion-based to some, but input from instructors or past-students with a similar experience would fall under 'specific expertise' and thus I think insightful answers are possible.

This is a pretty broad question. What part of the flight were you disappointed about? What were you expecting? How did the flight not meet those expectations?

The instructor rushed the lesson through and didn't really explain things. I expected at least a few minutes talking explaining various parts of the glider and their functions, but he just showed me the controls (not even all the instruments) before we took off.  More important, no explanations. e.g. he just told me the ailerons and rudder should always be applied together, but didn't tell me WHY or the consequence---"this and this are always done together!" (hence my previous question)  Basically, after that short lesson, I came back immersed myself on Internet to learn by myself.

That's a common complaint. Seems like bad instructor. Teaching is a special skill, and a fine professional/pilot doesn't make a good instructor. Yet many career pilots go through the instructor stage. On the other hand, perhaps you should have told him that you were interested in the details and insisted on asking why. Instructors work with different people and know that not everyone is curious, and don't necessarily want to open from the first lesson...

I do hope you'll keep posting questions here. I don't have a PPL-Glider yet (I only have 7 hours in gliders), but I'm excited to share what I do know!

For somewhat the flip side of this, you might be interested in First actual flight lesson, what to keep in mind? Full disclosure: My own question.

It'd also be helpful to know where you're starting from: are you learning to fly from the beginning, or have you learned on power and adding a glider rating?  Your description seems like what I'd expect from the latter - after all, most of those parts are the same :-)

I'm a glider instructor.  The first lesson would have been introductory and if there weren't any soaring conditions, I'm guessing the flight was pretty short, less than 15 minutes, so you probably did/saw a lot less than expected.  It's a challenging instructing environment because of the time limitations on no-lift days.
If you were disappointed with the instructor, note that in glider club operations you will generally fly with all of the club's instructors at different times and you will end up with a couple of favorites.
At least give it enough time to experience a good soaring flight with an instructor to find out what the potential is, and whether you think you can get hooked on the "game" you play with the atmosphere to stay aloft.  Some pilots get into it, some don't and would rather go with power.   Not much different from sail boats vs power boats. Me, I like both but if forced to choose, I'd go with soaring as a fun activity.
Assuming you are into it because you are interested in the sport of soaring, you should hang in until you are solo and get a good soaring flight by yourself.  The first thermaling flight on your own, climbing in many tons of rising air, is an incredible rush, more than first solo in my opinion.  Of course it all hinges on whether you get hooked on the game itself, of working the air to climb.
No two flights are ever the same.  Watch the private owners go out in their high performance machines and disappear for an entire afternoon.  4 hours in a glider is not like 4 hours in a power plane that beats your brains in with noise and vibration; it's like 4 hours of meditation - you return very relaxed and mellow.
Even if you don't think you'll take to the sport, and you plan to learn in power planes at some point, learning to fly gliders first will make you a far better pilot with respect to basic stick and rudder skills, speed control and energy management, so it's worth sticking it out just for that.

How does the safety of gliders compare to that of powered light aircraft?

I would say much safer statistically.  Discussed here: https://aviation.stackexchange.com/questions/51566/are-there-any-data-on-the-safety-rate-of-gliders-vs-single-engine-ga-aircraft .  The pilots of single seat private gliders generally wear parachutes.  This is because of the risk of midairs in competition with numerous aircraft crowding into single thermals, not because of the risk of the glider itself falling apart.  The vast majority of glider fatalities would be stall spin accidents coming in to land.

Thanks @John K , I did have a look at that question, but I don't feel a satisfying answer has been provided. Thank you for the response though. I'm guessing the chute won't save you from those low altitude stalls either...

It would help to compartmentalize your approach here.  When around the plane and especially when flying, do what your instructor says!  It is extremely important to build that trust.  Put yourself in the instructors shoes.  They have no idea what a new student will do and are literally risking their lives taking you flying.  Don't forget crashes and fatalities are a very real part of aviation.  Don't expect extensive explanations while flying.
Do save your questions for post flight discussion and make this part of each lesson.
It would also help to commit to a program (flying school) towards a goal (pilots license)
and spend time in class learning theory.
But for an intro, they are most likely just taking you up for a ride and seeing if they can work with you.  Yes, some will see you as a one timer and not treat you the way you like, but it's a two way street and it certainly will take more than one lesson to learn everything.
Once you find an instructor you are comfortable with and commit to a goal, you are on your way.  By all means, don't expect it to be completely your way.


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How to deal with turbulence while flying glider? (Cautions in applying rudder)
I just watched video explaining how the American Airline Flight 587 crashed

It led me to think about glider flying. The cause of that crash was that the first officer aggressively and unnecessarily applied full rudder left and right in turbulence, the air force against the moving rudder stressed the vertical stabilizer and caused it to snap.
Is such risk realistic in glider flying? If one encounters air turbulence in while flying glider, how to deal with it, and what to avoid?

Everyone chooses what to worry about. I would not choose to worry about this.

Is such risk realistic in glider flying?

What does "realistic" mean to you?  If it means "could it happen" then sure, it could.  Plenty of things could happen.  If a possibility greater than zero is all it takes for you to worry then by all means, stop reading.  Don't forget your shark armor and anti-meteor hard hat when you go out next.
However, most people consider "realistic" to include likelihood. Is it likely? Well, I searched through the last 8 years(1) of the NTSB accident database for glider accidents involving the term "breakup". Of the three relevant results, two involved aerobatics.  How many glider flights have there been in the last 8 years? Probably plenty of them.  Do you plan to do aerobatics?  If not, then your accident statistics are one in plenty.  Only you can decide if that's too scary for you.
It is not on the NTSB 10 most wanted list.  I have not read about it in FAA Safety Briefings.
In my experience, new students don't know what is important, so as a proxy, they worry about things that are vivid.  In-flight structural failures that have videos made about them are highly vivid.  That's why my original answer started out by saying "this is not a valuable use of your attention".  If I were your instructor, I would advise you to focus your concerns on flying proficiently and learning good decision making.  If you do that, the concerns here will take care of themselves.

If one encounters air turbulence in while flying glider, how to deal with it, and what to avoid?

There is no "if" here.  You are definitely going to encounter air turbulence. That's how you know you're doing it right.
How to deal with it? Pay attention to your instructor, monitor your attitude, remain calm, and fly the aircraft.

(1) - Why 8 years?  Because I got bored.

Do you have some sort of source for all this? Your answer seems just as believable if I replace "vertical stabilizer" with "wings", and yet breaking the wings is a realistic hazard. Frankly, I have no way of knowing whether this answer is completely right or completely wrong.

Sorry but I find the first part of the answer totally unacceptable:
"Authorities would not allow them to continue flying
Insurance providers would refuse to insure them
Instructors would refuse to fly them" This is like answering "Can I be sick if I eat xx" with "No, because if you could be sick then you would not be allowed to eat it."

@gadfly - I've updated my answer. However, I interpret your example about food as supporting my point. When I eat at a restaurant I don't ask if the food is safe because I trust that procedures are in place to prevent them from serving food that is unsafe.

First of all please put out of your mind "the first officer aggressively and unnecessarily applied rudder".  The pilot did what he was trained to do.  "Agressively" applying rudder can save your life if you are in an incipient spin.  The rudder is your friend.
Equally important, the pilots must be familiar with the limitations of the aircraft.  One cannot fly outside the safe envelope, which includes abrupt maneuvers which overstress critical components and can lead to catastrophic failure.
But there may be more than meets the eye here.  Hopefully the design of the tail and maintenance records were checked as well.  Although the aircraft mass played a role in isolating the stress to the tail (larger aircraft will accelerate more slowly to force: a = F/m),
as compared with a smaller trainer, one might expect the tail not to fail.  A B52 bomber famously lost most of its vertical stabilizer to wind side loading and actually landed safely.
Air turbulence can be very powerful.  Wake from a 747 is literally tornado like and needs to be avoided.
With a smaller aircraft, tail failure due to rudder application is not high in the risk department, but LOOK FOR CRACKS AND FATIGUE while doing your pre-flight and try to avoid conditions that may exceed the design of your plane.


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Do you need strong muscles as far as applying the yoke is concerned, in order to be able to deal with some emergencies?
In some of the plane accidents, the pilot had to use all his might to apply the yoke in certain direction to save the plane from imminent crash; in some cases even crew members had to help with the force. So it seems certain degree of physical strength is needed to be a pilot in view of possible emergencies, though it doesn't seem to be explicitly required?

Related, maybe a dupe?

For the Airbus it is not actually require any strength, all the technology is fly by wire, this means that the actual control (Side stick) is not directly connected to any cable, so been this said, there is no actual force to fly any airbus plane. For the Boeing plane, at least for the 737, that's the one I know, when it loses all the hydraulic systems, the aircraft will become on a manual reversion mode and it will need strength from the pilot to move the aircraft controls that are linked to the surfaces by cables, but this is a remote possibility to happen, and if it is the case both pilots can apply force to the control column

While generally true, it's not correct to say "there is no actual force" required for FBW. Maybe not "actual", but some "simulated" force is required: the controls are artificially loaded so that control was comfortable. This most comfortable force is not zero at all: we rely on force feedback in our muscles to gauge the amount of control precisely. More to it, if the control was too light, it would be too easy to pull a high G accidentally. Su-27 (a fully FBW aircraft) has a particularly heavy stick for roughly this reason, and the pilots not used to it do get tired.

The force on the side stick is very little, as it is done by the wrist and not by the full arm (Airbus recommendation practice) so to move the side stick requires a little effort or physical strength, check this web site and look for Pilot correct seating https://www.airbus-win.com/

It's true one doesn't need 'physical strength'; I'm just saying it's still not correct to say that there is 'no force'. A lot of research went into establishing what force (and other characteristics such as damping) would be comfortable for this sidestick. In fact, we control by force, i.e. a certain pressure on the stick results (ideally) in a certain control effect (e.g. vertical acceleration in normal law).

Most transport category jets have hydraulic flight controls where the forces the pilot acts on are through bungee spring devices (a pitch feel unit) in the control cable circuit.  For certification, pitch feel units normally limit the force required to move the column to full travel to 50 lbs at high speeds and less than that, say around 30lbs, at low speeds (they are intended to simulate the increase/decrease in control resistance with speed that is felt with manual controls).  Most pilots, even small framed males and females, can pull 50 lbs, although sustaining that for more than a few seconds can be a problem. But, there's someone beside to help.

Someone, like, the Trim Daemon? ;)

Your FO.  If you're lucky, when you get a trim runaway it's nose up so the other pilot can jam their leg against the column to help push.  Nose down requires you to take turns pulling.  I've done it in sim training and by the time you land your arms are like lead anchors.

@ John K would "trim runaway" be referring to excessive up or down trim to compensate for out of range CG? (I'm starting to like the Chinook).

No it's when you have electric trim and something happens where it runs on its own until you stop it ,or it gets to full travel.  It's a normal training item on jets.

Curious, are jets trimming themselves these days?  This would be airliners, I guess the answer would be yes for the B2 bomber.

Just about all autopilot systems operate the trim system to limit continuous out of trim pitch loads.  The autopilot servo will hold a little bit of out of trim force, but once it exceeds a threshold it commands a trim change.  If you dial the speed bug down when on AP in speed mode and the airplane slows you will see the column come back, then the trim indicator will move as the AP retrims to limit the continuous load on the AP pitch servo.

Not all planes have two pilots, though, nor crew members. What if you are alone?

I'm talking about large multi crew aircraft.  For light planes with manual trim, the chances of getting into that kind of pickle are microscopic.  I sure there are scenarios however, like flying single pilot on say a Piper Navajo with electric trim that runs away and can't be stopped before full travel, well.. you're on your own.  In any case, that kind of emergency is extremely rare.

This question really is way too generic to be easy to universally answer.
The amount of force required to operate the controls of different aircraft under identical conditions is different, varying from very little to requiring some serious muscle.
Now apply that to a wide range of potential emergency scenarios.
At the one end we have emergencies where no amount of force will change the outcome either because the relevant controls are no longer there (ripped off vertical stab anyone?) or because their use is irrelevant to the emergency (landing gear not extending on approach for example).
On the other end we have emergencies where the controls are jammed but can be moved manually if only enough force is applied to them (e.g. the hydraulics failed, leaving the controls stuck in a high deflection position but they can still be moved if you are strong enough). THAT would require a serious amount of muscle most likely.
But it all depends on the aircraft, the emergency in question, and the flight regime in which the aircraft finds itself when considering whether any amount of input at all will save the day, let alone brute force.

The note on failed hydraulics reminds me of Reeve Aleutian Airways Flight 8.

It would be very helpful to narrow this question down as to whether or not "physical strength" is needed due to a failure of a built in mechanical/hydraulic system
(like losing power steering in your car), or simply in a cable driven control surface system, found in recreational aircraft.
Enormous physical strength is NOT required to be a pilot, although good mental and physical condition is a must.  Endurance of concentration and stamina of strength do help as you may be required to "go around" after a long flight.
More strength is needed at higher speeds due to aerodynamic forces, but that is part of Vne.  Please do not imagine three people tugging at the controls to save a Piper Cub.
So, depending on your abilities, careful research and expert instruction will get you going in a plane that suits you.

Need an explanation for downvote, unless we are into the discriminatory "upper body strength" mode of thought!  For what reason was this downvoted?

If a small plane, connected by cables only, is not trimmed properly, it can indeed take some good arm strength to overcome what the plane wants to do, generally pushing or pulling, until you can get the trim set up. Slowing down by throttling back can help also. Turning, not so much strength is ever needed. Just getting out of dive, or overcoming a strong climb when full power is being applied - you don't want the plane to climb up into a stall on you.

My biggest problem in the 172 was making sure the seat pins were locked properly, so I would not slide back while climbing out!  But as far as strength, it will depend on the plane.  Before hydraulics, cable driven systems had counter weights to help make it easier.  5 foot 1 inch Hanna Reitsch flew the mighty Gigant transport aircraft, though she did have some muscles from all the flying she did.  I would not discourage anyone with average strength to fly, especially recreational.

BTW getting out of a dive - chop throttle first.  Overcoming a strong climb - ease up on throttle and push forward.  The trim wheel is easily spun.


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Why are months (e.g. December) used to notate a runway?
I'm writing a report on runway quality and I've stumbled onto a weird qualifier in the data. I understand that runway 17/35 indicates which direction the runway is facing based on magnetic heading.

RWY_ID 17/35 17/35 26-Aug 14/32 30-Dec 28-Oct 21-Mar 13/31

What does 21-March mean for example?

Where did you come across this data? Context might help. Please [Edit] your question.


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What is the cheapest plane one can buy to fly above Mach 1 and be able to pull 8g plus?
Which plane would you suggest for someone who would like to be able to fly fast enough to break the sound barrier, yet also be able to pull lots of Gs?
What would be the price of such a plane, and how much would it cost per hour to run and be maintained?

You know how much training/equipment it takes to pull 8g without passing out, right? Most mortals (that is - non fast jet pilots) pass out below 5g. I've done about +3.5 sustained for a few seconds, and it was harsh.

Maybe a MiG 17 in a dive.  I've seen them listed for <$100k.

One thing to keep in mind with speed is the FAA regulations. In the military when jets take off they can go however fast they want because they are under the DOD. Under the FAA they have the 250 knot limit under 10,000, you can't fly supersonic over land without authorization, etc.

Not however fast they want, they are generally waivered for a specific safe departure speed below 10k' in accordance with their performance envelope.  Also, why 8 Gs?  That is a pretty ridiculously painful "goal" to shoot for.

Ignoring the various practical limitations that 99.9999991% of people would encounter....
The answer more has to do with what is available than what would be optimal. There are not a whole lot of air frames that fit such a criteria and there are even fewer that are for sale to/in the public hands, when talking about things that exist in the single digit realm for-sale quantity is a real factor.
This McDonnell Douglass F-4 is currently listed for 3,950,000 USD and perhaps gives a good basis for what such a plane would cost. The F-4 carries 3335 gallons of Jet fuel, at my local field where fuel is a reasonable 4.50 a gallon its going to cost you 15000 USD to top off the tanks. Fuel burn depends on how you run the aircraft, if you are slamming it at super sonic speeds all the time your hourly burn rate is going to be high.
Maintenance is harder to pin down. These jets were generally operated by the military so you are going to need to find a mechanic out in the world that is willing to deal with it. You may get lucky and find someone who has some military experience to do the work but if you cant you are going to need to hunt down all the maintenance manuals and related documentation for the aircraft which may be harder to come by than you think. On top of that you need to keep two J79 in working order that may already have a lot of time on them.
If you want to hop to the other side of the pond design wise this MIG-29 is listed for 4.60 Million USD and will get you into the super sonic spectrum and allow you to pull some G's.
So for ~4.5 Million and some non determinant maintenance costs, lets say conservatively 500,000 a year for fuel, oil, incidentals, maintenance, some new tires, avionics and other odds and ends you can have all the fun in the sky you want.

"various practical limitations that 99.99999991% of people would encounter" So you're saying there are right around 7 people in the world who could design an airplane that can pull 8 g, or who can pull 8 g using such an airplane? That seems rather on the low side.

@MichaelKjörling Ive removed one of the 9's but even if there were thousands of people with the physical ability, proper pilot certifications, and most importantly, money to own something like this privately there simply dont seem to be that many available at market.

The other problem is that it would be an exhibition category aircraft...

@RonBeyer How is that a problem in the context of the question asked?

The F-4 is hardly the right tool for the job. The Mig-21 and advanced jet trainers are smaller and cheaper while delivering the OP's requested performance. As for the difficulties for 99% of the people, former jet pilots are a fairly large group that would be capable of doing it.

With the right training & conditioning & a good G suit, 9 G's in an F-16 isn't so wildly cosmic that only 0.00001% of everybody can handle it. Far from it. Not Joe Average from Main Street going up tomorrow with neither experience not training, but somebody with the $$$ to operate such a jet can certainly get what's needed in those departments. I would question, though, if an F-4 has anything like the operating limitations to pull 8 G's, even briefly.

Probably a MiG-21.  Some flyable examples are available for between \$50,000-\$200,000, though I suspect some those airframes in an excellent condition will run upwards of \$1 million.
Operational costs for MiGs tends to be surprisingly cheap, though considerably more expensive than operating exotic sports cars or other millionaire toys.  At an estimate, I would guess $3000/flight hour for a MiG-21 and it all depends on what equipment is aboard eg hot ejection seats, etc.
Other popular types are L-39s, Folland Gnats, A-4s, F-5s, T-38s, even a Panavia Tornado and a Harrier on the market.  They can run from $200000 to tens of millions of dollars and cost thousands of dollars an hour to operate, depending on type.
But aside from the purchase price, if you’re a newbie to flying, it’s gonna be a while until you are legally capable of logging PIC time in one of these jets, at least in the US. The FAA has specific guidelines on piloting these kinds of Experimental category surplus military jets, which have to be followed.  See AC 91-68.  You’ll need at least 1200 hours TT plus at least an existing PPL rated for the category and class of aircraft, then undergo further training and pass a practical test to get an LOA for PIC operation of these kinds of aircraft.  Type ratings also apply, if the airplane in question meets the characteristics listed in §61.31(a).
I can’t speak to Peter Kampf’s comment; other countries may allow you to fly such an aircraft without additional training or aeronautical experience requirements but keep in mind that going into this kind of an aircraft, it is a hot blooded machine that demands to be flown by the numbers and will not suffer a fool or a neophyte at the controls.  While it is true that military forces throughout the world allow their pilots to operate these airplanes at far lower time levels, in many cases they pay for it through the nose with a high accident rate. The USAF alone in 2018 had 716 mishaps with 19 fatalities during flight operations.  More that 15,000 US military airmen were killed in flight training accidents during WWII.

The MiG-21 is a very nice-looking plane, and sure it flies quiet well. The prices you quote seem rather low, but securing a proper maintenance for that plane will probably be a very expensive nightmare...

There are companies in the United States which do R&O services on MiGs.  Spare parts and technical on MiGs is also quite cheap due to how it was manufactured in the Soviet Union.

@xxavier Station the airplane in an East European country where there are still lots of people with MiG experience. The tickets to travel to your plane will be a vanishingly small part of operation expenses. Also, in some countries you don't even need a flight plan for aerobatic flights. However, some parts like the engines need to be shipped to the manufacturer for major maintenance, which will become very expensive quickly.

Offhand I'd question if 8 G's is allowed for the MiG-21. Not questioning if you can pull it (the question doesn't require "sustained" 8 G's), but if the aircraft is built to do so without risking damage. Lots of supersonic jets have G limits in the 5-6 G range (the T-38 comes to mind); what are the limitations on the Fishbed?

From your other types list, L-39, Folland Gnat, A-4 and Harrier are all subsonic, so don't satisfy the criteria in the question. Only F-5, T-38 and Tornado are supersonic.

@RalphJ, T-38 is a trainer, it does not need high G, but MiG-21 is an air-superiority fighter designed at time where guided missiles were unreliable and maneuver combat was still essential. It's hard to find a reference, but I found one saying it's limited to 8G up to M0.8 and 6G above, and another according to which it has just about enough lift to pull 8G at M0.75 to M0.8.


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What measures prevent a military aircraft's weapons from being fired on the ground?
Recently the 20mm cannon of an F-16 was accidentally fired on the ground by maintenance personnel at Florennes Air Base in Belgium, resulting the the destruction of another F-16 and damage to a third.
https://theaviationist.com/2018/10/14/f-16-completely-destroyed-by-another-f-16-after-mechanic-accidentally-fires-cannon-on-the-ground-in-belgium/
What measures do  military aircraft have to prevent their weapons from being fired while the plane is on ground?

Normally with aircraft there is a sensor called a weight on wheels switch.  This tells the computer that the aircraft is on the ground.  The computer (or a system of relays for older air frames) will prevent any system that was designated by the owner, or required by regulations, from activating while in the ground.  Also as a secondary preventative measure certain mechanical systems are also pinned in place after landing to help prevent ground actuation.  However if it happened during maintenance it is very likely these systems were disabled to perform system maintenance on the cannon.

Your answer is far better than mine. Still begs the question - why were they doing maintenance on an armed aircraft?? That, however, is a different question.

But do you actually know whether weapon arming is tied to the squat switch on fighters? It would be somewhat unexpected.

The article quoted implies that there is a sensor in the F16 to detect when the undercarriage is lowered, which functions as a a gun safety switch, but there is presumably provision for overriding this in order to perform gun testing.
A variety of technical and procedural measures are designed to ensure safety with aircraft gun armament, the details varying with the specific type of weapon. The M61 20mm cannon will not function without electrical power, it is electrically rotated (when internally mounted) and fires electrically primed ammunition, so switching off the power should prevent accidental firing with this gun. Other types of cannon with reciprocating mechanisms, such as the 30mm DEFA 550 series have to be cocked or armed before they will fire, a common procedure is to prohibit pilots from doing this until the aircraft is airborne.

What, you can't test a gun in flight?

It would be less expensive and quicker to test it on the ground if possible.

Ok, for the F-16 to fire the gun on the ground you need, Ammo, electrical and hydraulic power, hold back tool removed, electrical safety pin removed, rounds limiter set to off or at least 100. No avionics need be powered. Master arm to arm, ground Jett to enable. Squeeze the trigger. The gun will fire until the last round switch opens because it’s out of ammo, the rounds counter if set to on hits zero, the security police shoot the guy sitting in the cockpit.
The Belgium accident had 2 major Tech Order violations.

ammunition installed during gun operational check. Without ammo, a technician will need to hold the last round bypass switch to on. FWIW that switch is just forward of the gun housing so if someone was holding it they are most likely deaf and or burned pretty bad.

gun holdback clearing tool installed and gun rotated to clear rounds from the firing cycle.

It’s been 30 years since I did my last F-16 gun ops check and I still remember how to do it and not get killed or shoot the place up.
Also to correct some other posts. The gun is electrically controlled and fired. It is rotated by a hydraulically powered motor.

@ymb1: Manually holding the switch is dangerous with ammo, because the holder would be right next to the firing gun.  No ammo = no firing = not dangerous.

There are also physical safety switches, that date back to when weapons were first mounted on aircraft. Still present on modern armed aircraft. On the F16, a switch on the joystick controls selection of missiles or gun. One of it's positions is 'safe'. Obviously, that switch on the Belgian F16 wasn't in the safe position.
During WW2, there was a real problem with aircraft landing on a carrier, and the guns being discharged accidentally when the jolt of the landing and arresting caused the pilot's hand to hit the trigger on the joystick. Consequently, landing on a carrier with the gun switch not in the safe position was a serious transgression that would land a pilot in real trouble... you could kill a lot of deck crew if you discharged six .50 cal machine guns across the deck.
Even so, accidents can happen. On July 29, 1967, the USS Forrestal was seriously damaged when a Zuni air to ground missile was accidentally discharged from an F4 Phantom, striking an A4 Skyhawk waiting to take off. Piloting that Skyhawk was a young navy Lt, John S McCain. While the missile didn't detonate, it did tear open the Skyhawk's fuel tanks, starting a major fire, which led to a 1000 pound bomb detonating. 134 sailors died as a result, and hundreds were injured. It is believed that a short circuit of the firing mechanism led to the missile being discharged.
Aircraft carriers in particular can be quite dangerous. They combine high performance aircraft, high speed takeoffs and landings, plus all the fuel and munitions that the aircraft will carry, in a fairly small space. The fact that aircraft carriers don't blow up more often is a testament to the quality and discipline of it's crew.
Since the Forrestal incident, there have been no repeats of missiles being accidentally discharged on a carrier deck. Whatever measures were put in place after that, appear to have been effective.

The gun would not have been fired by accident. The mistake here is that they did not unload all live munitions to make the aircraft safe before functionally testing the weapons system. There are multiple safety interlocks that stop a gun from “just firing”.

The undercarriage being down and locked or weight on wheels (WoW) is the first.
There will be a Master Armament Safety Switch that stops the armament control system from being powered. (It will have to be set to live during testing and when releasing stores in anger or jettisoning them in an emergency). (Some aircraft also have a standby position to carry out self testing prior to flight).
the guns selected on the weapon control panel.
a switch called a late arm switch set on.
then the trigger depressed.
In modern aircraft navigation/weapons computers also have to be turned on and a target has to be selected before a commit to fire signal gets passed to the gun/store.
some gun tests also require the gun to actually be electrically disconnected and a test box connected in its place with LED’s to show the gun firing pulse is being received.

To fire on the ground WoW override tools would be used, some aircraft have BUTTS switches or armament ground test switches to trick the computers into thinking the aircraft is in flight. The aircraft nav computers will need to be turned on with potentially a dummy flight plan loaded.

You seem to know your stuff and this is a good answer, except for that first sentence.  I understand you mean that there are many steps required and the gun couldn't simply "go off", but if you read the sentence by itself it implies that the actual discharge of bullets was intentional.  But of course, it was fired by accident.

A lot of fighters have some kind of a "Master Arm" switch that brings the weapons live as well as activates some other related functionality. As discussed by this former F-15 pilot in the podcast 224 – Flying the F-15 Eagle its flown in the off position 99% of the time. There is also some discussion about HUD functionality related to the master arm options in this thread (but its Reddit so take it with a grain of salt).
In this article about refueling the F-15

As the fighters approach, they will be asked to “check nose cold and
switches safe.” That simply means that all emitters are off, to
include the IFF system, any ECM pods, and the radar is placed in
standby mode. If the approaching receivers were in a fight prior to
the rejoin, it’s critical for them to have their Master Arm switch to
the OFF position and thereby safing any remaining stores aboard.

Depending on the airframe, they may slo simply unload the ordinance to prevent accidental discharge.

Depending on the platform, the master arm switch may also disable all high-power EM transmitters as well as countermeasures. But again, depending on platform, there may be a ground override switch to bypass weight-on-wheels to allow master arm to be enabled on the ground =/

According to the article you linked:

the use of the onboard weapons (including the gun) is usually blocked by a fail-safe switch when the aircraft has the gear down with the purpose of preventing similar accidents.

It seems it isn't quite so "fail" or "safe", at least in this instance.

It seems more like fail-to-safe.


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Is any convention to tell the propeller rotation direction of an airplane?

Here are two airplane with single and dual engine.
From single engine airplane we know there is TURN LEFT tendencies. There are four tendencies (Torque reaction, Precession, Slip Stream, and P-Factor) caused by the propeller rotation, which it rotate clockwise seen from the tail to the nose side. If the rotation is opposite, probably the name will be TURN RIGHT tendencies.
Then my question, is any convention to tell the propeller rotation, such as, rotation is must be seen from tail or pilot side. I.e:

Clockwise, mean the propeller is rotates clockwise seen from the tail nose side. Vice versa:
Anti/contra/counter clockwise, mean the propeller is rotate anti clock wise seen from nose to the tail side.

The four tendencies are like confirming that the rotation is clockwise seen from tail side to the nose side. But however, I need a valid info regarding this, which expected the convention is applicable to another airplane with multiple engines/propellers and it will confirm that no need to tell where our stand point when saying the propeller direction. It is enough to say, clockwise or anti/counter/contra clock wise.

When you say "clockwise" or "counter-clockwise" it is generally accepted that this would be the view as if you were standing behind the aircraft. Unless it is otherwise stated, this is the convention that you can assume.
If you need a way to tell by looking at the prop, the thicker part is the leading edge. In the first photo you posted, this would rotate counter-clockwise from the perspective of the photographer, or clockwise from the perspective of behind the aircraft. This is, by convention, a clockwise rotating propeller.

When you say "clockwise" or "counter-clockwise" it is generally accepted that this would be the view as if you were standing behind the aircraft. Unless it is otherwise stated, this is the convention that you can assume. Thank you for this confirmation.

That's why I ask this question as perfective of photographer is different than convention. To know the convention will make easier to tell every one without to complicated explanation.


text:
Do contra-rotating propellers have the same RPM?

Image source
Here is a contra-rotating propeller. The front propeller rotates counterclockwise while the back propeller rotates clockwise. My questions are:

Do they rotate at the same speed (RPM)?
If not, which one is rotate faster, and why?

Most if not all contra-rotating propeller systems are geared together so that both sections turn at the same speed.  This is done so that as well as allowing effective conversion of very high power into thrust, torque and P-factor are cancelled, making the aircraft easier to fly (especially in a single-engine or two-into-one installation).
This is why you see the same diameter propeller in front as in the rear -- if they were turning at different rates, the slower one could be larger diameter (a limitation on diameter is transonic conditions at the tips) -- but you always see the same diameter on front and rear.

Thank you for the explanation. It make sense if one is longer than another, then the longer one must be slower.

It depends on the power source.

a single piston engine driving both props (as shown in the image in the question): they're geared together so rpm will be the same.
two turbines driving one prop each (e.g. Double Mamba): no coupling between the engines, so prop speeds may be different. You could even shut down one engine in flight (for low-speed, fuel-efficient cruise). The speed of each prop depends on the throttle setting of each engine, so the pilot can run either the front or rear prop faster, or have them both at approximately the same rpm.
Compound engine driving both props: the Napier Nomad drove one prop from the crankshaft, and the other from a turbine. While RPM would be related, they wouldn't necessarily be identical.

The Russian Bear bomber has one turbine driving each propeller set, as I recall -- and works like a single piston engine, gears to drive the two props off the same output shaft.

@hobbes, I am quite confuse to your answer. Just back to my question: Do they rotate at the same speed (RPM)? and If not, which one is rotate faster, and why? MY question is NOT about how the work.

My answer is that the rpm difference (if any) depends on the aircraft you're looking at. On some aircraft, the props are geared together so they always run at the same speed, on other aircraft the props are independent so prop speeds are up to the pilot. For the aircraft you've shown in the question, the props are geared together so they run at the same speed.

That nice that they propellers are not rotating at the same RPM. But which one is rotate faster in the case they are not rotate at the same RPM and why? That is my second question.

I've already answered that.

No, not all contra-rotating propellers turn at the same rpm.
Take two russian (very famous) examples, the Tupolev TU-95 Bear, and Antonov AN-22 Cock (go figure...). Both use versions of NK-12 turboprop engine, and as can easily be seen in many videos available on the internet, their propellers are not geared in a way that would make them turn in equal rpm.
TU-95 propellers turning ratio is such, that for each full turn of the front propeller, the one behind turns a little more than half a turn: TU-95 engine start on Youtube.
For AN-22 the ratio is one full turn for front prop, and about 3/4 for the rear one: AN-22 engine start on Youtube.
As for the reason of this, I have no knowledge about that. My more or less civilized guess would be that it has to do with load distribution between propellers, and maybe something to do with vibrations and resonances of the powertrain.
The aforementioned ratios can be seen during engine startups, but if the propellers are geared together, the ration will of course be fixed througout the rpm range. There has been speculation that the props on NK-12 are driven by separate turbine shafts (not making their rpm's physically connected at all), but I have not been unable to   prove this wrong or right.

"TU-95 propellers turning ratio is such, that for each full turn of the front propeller, the one behind turns a little more than half a turn: TU-95 engine start on Youtube."  During initial startup, yes, but this disappears once the engine core reaches operating speeds.  You would see interference patters in the props and create nauseating vibrations and noise pulses if it did not.

Have you whatched the videos? There are all kinds of interference patterns during and after startup, it actually has more to do with the camera used than anything else... If the propellers are geared together, how would the ratio be changed after start? And more importantly, why?

The props may not be geared together, but make use of independent propeller govenors to maintain a constant, equal speed between them during operation.  Yes I watched the videos, but as I said in the first comment, watch for interference patterns once the airplane is ready to taxi.  You won't see them.

And as I said, the interference patterns are dependent on the camera. They may not be visible because of the frequency being such that the camera is not able to capture it. I would gladly accept being proven wrong here, if undisputable evidence was presented. Is it possible to drive two propellers from a single shaft with variable rpm ratio, if yes, how? If not, why?

You could but why would you want to?  See my answer below.

You might want to if the setup thus was more efficient. I admit that I do not know either way. You have not presented any hard evidence in either direction.

For the aircraft in the picture ie a heavily modified P-51 unlimited racer driving a Rotol Contra Rotating propeller, the answer is yes.  Both propellers are geared off the same crankshaft and turn at the same speed.
All contra rotating propellers turn at the same speeds during operation.  If not, it would negate the purpose of the setup, that is to eliminate a net P-Factor, spiral slipstream and engine torque effects.  They would also cause nauseating pulsing noises in the cabin which become very uncomfortable after long periods.

The second propeller encounters airflow affected by the first propeller. For the P-factor to be balanced out, the propellers would have to be turning in same rpm, pitch and airflow. Change any of these, you have to modify something else too, like rpm for instance. And  by the way, TU-95 is famous for its noise and vibrations.

Properly designed a good contra rotating propeller will cancel out P-factor, or significantly reduce it.   I’m not buying that Tu-95 operates with one of the propellers turning faster than the other one is. This is a colossally  stupid design and extremely wasteful in terms of additional drag.  That fact that makes noise and vibrates is irrelevant.   Soviet military hardware was brutally functional.

You are aware that there are propfans with different number of blades between propellers. How does that differ from having two different rpms? The second prop gets faster airflow pushed by the first prop + at a different direction. You don't have to buy my claim, you just have to prove me wrong. Should you do so, I will be totally fine with it

.....do said propfans operate in a contra rotating fashion?  Do they have the same polar moment of inertia?  What about blade area?  Little bit more here than meets the eye.

The fan blades turn in opposite directions, yes. As for the polar moment of inertia, I have absolutely no idea.

What meets my eye in the videos is a clear difference in rotational speed. So as per question, well, all CRP's do not have equal rpm between propellers.

From another question a comment by @Koyovis : " Why would torque be an issue in a 4 engine plane?" There  obviously are priorities involved in designing a CRP. First priority is efficiency: how do you get the best performance (thrust & fuel consuption) out of the setup. Only after that do you handle the torque or P-factor, because a lot of them is already taken care of by the CRP anyway.

From efficiency point of view, counter-rotating propellers are worse than a single propeller. Exception to that is counter-rotating rotors on some helicopters where there is enough vertical separation so the upper rotor stream contracts and some fresh air is feed to the bottom rotor. As airplane propellers would work most of the time at high speed, the influx of fresh air is lost, the second propeller is operating in the stream of increased velocity, and so the efficiency is less. To answer your question I'll need more information, as what you want to achieve. For example if the goal is to eliminate torque, the rear propeller needs to rotate faster. If the goal is to reduce fuel burn then one propeller needs to be stopped and feathered.

What is your source for counter-rotating propellers being less efficient than single propellers? This paper cites two studies showing at least 6% better efficiency for CRP: https://www.rcgroups.com/forums/showatt.php?attachmentid=2815700

Turbulence from the front blades may reduce efficiency of the rear blades, but in cases where you have too much power for a single propeller to handle at RPM that gives subsonic tips, a contra-rotating setup is a lot more efficient (and quieter,and more durable) than a single propeller with supersonic tips.


text:
What should a pilot do when facing a sudden tail, cross, or head wind?
Consider a pilot is flying a conventional fixed wing airplane with a ground speed of 60km/h with no wind. Then suddenly the wind starts blowing at 20km/h in either of the following directions:

from back to front (tail wind).
from front to back (head wind).
from left to right (cross wind).

What should the pilot do to maintain speed and altitude in each of the possible situations above?

Could you explain how will the wind blow simultaneously from opposite directions? Are you talking about gusts?

I didn't say the wind blows at simultaneously. They are three situations that could be happen.

I've edited the question to make it clearer that you are asking about multiple distinct possibilities.

Is this at altitude, or on approach or take off?

Could be at any condition. Any condition will be affected. But better to consider during cruising or altitude.

@AirCraft Lover: Where will you find a conventional plane that can fly at 60 km/hr? That's 32 kts!  If it's a gust/wind sheer, you might stall, though in most GA airplanes, you'd already be in a stall.  Otherwise, you reduce power, add power, or change heading and add power.

I am downvoting this question as it makes no sense to ask about an aircraft that cruises at 32 knots. Please edit the question to something more reasonable.

Plenty of conventional airplanes can cruise at 32 knots.  For example, most any ultralight airplane.

@quiet flyer: I don't think ultralights qualify as conventional planes, pretty much by definition :-)

Many people stress energy and airspeed management, this is a good example.
Sometimes a strong gust can reduce airspeed faster than your engine can increase it.
The sudden tail wind gust is very dangerous near the ground. Increase throttle and pitch down. Use your potential energy plus the engine thrust to maintain airspeed.  Wind conditions found in microbursts can create this effect.  Constantly check airspeed.
A strong headwind gust has the opposite effect, causing a momentary increase in airspeed, and increase in altitude.  Rarely a problem, keep an eye on airspeed as the gust passes, continue to use pitch and power to control airspeed and altitude as needed.
Side gust effect will affect your heading much more than speed and altitude, as it's velocity change does not add or subtract from airspeed.  Effects here could include a sharp roll initially away from the gust, and the nose being pushed into the wind from side force on the empennage. A stable plane should mostly self-recover without significant loss of altitude.
The mantra "the plane just moves with the air mass" does not apply to gusts.  This is why pilots generally approach at slightly higher airspeed under those conditions.

The rule of thumb for approach is add half of gust windspeed to your normal approach speed.

I note this Increase throttle and pitch down. What is the intention of pitching down?

Instantaneous increase in speed.

Thank you for the explanation.

On encountering a sudden tailwind or crosswind gust on par with the previous airspeed, the pilot should immediately deploy the ballistic parachute to avoid crashing.  With an equivalent headwind gust, pulling up into a loop to dissipate the excess energy is often the best strategy.

How many conventional planes are equipped with ballistic parachutes?

Please refer to the rule #14